Coarse particles of such bulk products as coal, pelletized iron ore and limestone ordinarily carry quantities of introduced, surface moisture. For example, water sprays are commonly employed in mine crushing operations to minimize the quantity of dust or fines that is discharged into the atmosphere, and a certain amount of this moisture is picked up by the product being processed. Coal is also sometimes stored underwater to avoid both weathering and spontaneous combustion. Furthermore, atmospheric precipitation introduces moisture into products which have been stored in the open or shipped in open-top conveyances. Regardless of the source, surface moisture much in excess of about five percent can create serious problems when particulate products are transported in bulk during sub-freezing weather. Railroad demurrage charges encourage immediate unloading of freight cars and have prompted the application of vibratory and impact forces, thawing with blow torches and even resort, in extreme cases, to blasting in order to loosen and discharge solidly frozen bulk cargo.
Another aspect of the problem, particularly with references to the freezing of coal, involves the fraction of the cargo that has adhered specifically to the sides and bottom of the rail car. It has been observed in the field that coal freezing to the side walls and bottoms of the rail cars presents a severe problem. Often, the length of transit and the ambient temperature are such that the interior coal does not freeze; and as a result moisture can migrate from the warm interior to the cold rail car walls. This moisture contributes to the freezing which occurs on the walls and bottoms of the car. Also, in most instances, the loaded coal maintains a higher concentration of large particles nearer the walls. Because these large particles have less surface area to accommodate the surface moisture, aggrevation of the freezing occurs.
In the past, release agents comprising a light petroleum oil or a mixture of water and various glycols, with and without surfactants and other additives, have been sprayed or mopped onto the interior walls of empty railroad hopper cars, and sometimes mixed with the cargo itself, in an effort to reduce the compressive force necessary to dislodge a load of subsequently frozen coal or the like. However, it has been found that these prior art compositions quickly wear off or wash off the treated surfaces and thus are neither reliable nor economical.